Several criteria like conspicuity, legibility, and comprehension must be met for an icon to be effective. Previous studies found that visual and cognitive features of icons have significant influence on meeting the criteria for icon effectiveness. The aim of this paper is to present a review on visual features (color, shape, size) and cognitive features (familiarity, concreteness, complexity, meaningfulness, semantic distance). The influence of these features on icon effectiveness was studied. The relationships amongst cognitive features and ways to quantify cognitive features were identified. Suggestions regarding opportunities for future research on icons were also highlighted. Such a review would be helpful in formulating research plans and methodologies for icon studies in the future. In addition, this review would facilitate graphic designers to create more user-friendly icons in various contexts. © 2009 American Institute of Physics.